<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .divcss5{ width:400px; border:1px solid #F00; background:#FF0}
        .divcss5-left,.divcss5-right{ width:180px; height:100px;
            border:1px solid #00F; background:#FFF}
        .divcss5-left{ float:left;
           }
        .divcss5-right{ float:right;
           }
        .clean{
            clear: both;}
    </style>
</head>
<body>

<div class="divcss5">
    <div class="divcss5-left">left浮动</div>
    <div class="divcss5-right">right浮动</div>
    <div class="clean"></div>
</div>
</body>
</html>